1. Field of the Invention
This invention relates generally to limited slip differential gear assemblies used in transportation. More particularly, this invention relates to devices and kits to facilitate conversion of an open differential into a limited slip differential.
2. Problems in the Art
Wheels placed on opposing ends of power transmitting axles spin at different speeds during turns due to the longer path the outer wheel must travel during the turn while both wheels stay connected. The inner wheel must, by necessity, travel at a slower speed than the outside wheel.
Without a differential, the wheels connected to the powered axle would have to be locked together which would result in one wheel slipping in order to keep up with the other wheel. This would result in enormous strain on the power-train and would also result in an uncomfortable ride as one wheel slipped its way through the turn. The differential is designed to split the torque generated by the engine and transmitted through the power-train to the driven axle.
The simplest form of differential is the open, or conventional, differential. The wheels in this differential setup spin at different rates due to the fact that the axle is decoupled from the ring gear which transfers power from the pinion shaft to the wheels. Pinion gears (spider gears) are affixed to and turn with the ring gear. The axle is bifurcated and side gears are affixed to the internal ends of the bifurcated axle. The axle is re-coupled by seating the side gears into the spider gears, which lie in a perpendicular plane to the side gears. As the ring gear, which lies perpendicular to the axle, and affixed spider gears rotate around the axis of the axle due to the transfer of force from the pinion shaft, the spider gears distribute the power to the bifurcated axle sections. Since the spider gears engage the side gears so that the two side gears do not have to rotate at the same speed, the two wheels can thus turn at different rates without placing undue stress on the power-train. The downside is that the open differential always applies the same torque to both wheels. The maximum amount of torque is limited to that which will not make the wheels slip. Thus, when one wheel has no or little traction, very little torque is applied to the wheel with traction.
Limited slip differentials (LSD) were designed to limit the velocity difference between a pair of driven wheels, allowing torque to be transmitted as long as one of the two wheels has traction. The two main types of LSD are the torque sensitive (geared or clutch based) and speed sensitive (viscous coupling and clutch pack).
The torque sensitive clutch-type LSD is similar to the open differential but adds a spring pack and a set of clutch discs that are evenly divided between the two wheels. The springs push the side gears against the clutch discs. The clutch discs are in turn attached to the cage of the ring gear. The stiffness of the springs combined with the friction produced by the clutch disc on the cage keeps the wheels turning at the same rate and supplies equal torque to both wheels. The torque supplied to the slower moving wheel is equal to the amount of torque it takes to overpower the clutch disc and partially decouple the faster moving wheel from the power-train.
Limited slip differentials have become standard on off-road vehicles and high performance sports cars that are designed to handle hard cornering where one wheel may be slightly higher than the other. Golf carts often leave cart paths and become subjected to terrain that can leave one wheel off of the ground, or at least in less contact with the ground than the other driven wheel. Most golf carts have been and continue to be manufactured with open differentials. In many instances, it would be beneficial to convert an existing open differential on a golf cart into a limited slip differential.
An additional benefit of developing a successful means of wheel to wheel torque transfer is evident under braking. Since an open differential will allow the wheels to rotate at any given independent velocity, during hard braking one wheel will lock up before the other causing a dangerously unstable vehicle condition. On flat ground, this makes braking dramatically less effective and can cause the vehicle to spin out of control. When going downhill, this will cause the vehicle to “lose the brakes” and accelerate out of control or cause the vehicle to spin and potentially flip.